Energy monitoring in gins

Authors: Hardin Iv, Robert; Funk, Paul

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2011
Publication Date: 4/1/2011
Citation: Hardin IV, R.G., Funk, P.A. 2011. Energy Monitoring in Gins. In proc of Beltwide Cotton Conference. National Cotton Council. Atlanta, GA. January 4-7, 2011. CD ROM p. 636-645.

Interpretive Summary: Energy costs are the second largest source of variable costs for cotton gins, accounting for 27% of variable costs. Energy use has not been a major consideration in gin design in the past. However, electricity costs have increased significantly in recent years and will likely continue to increase, due to a limited supply of energy sources and increasing demand. Surveys over the past 50 years have shown that the average electricity use per bale has remained between 45-50 kWh/bale. Although the size of gins has increased significantly, the ginning industry has not become more energy efficient. Many of these surveys have demonstrated a wide variation in electrical energy use, with the least efficient gins using three times as much electricity per bale as the most efficient gins. Improved energy efficiency can result in significant savings for the cotton industry. In 2010, only a 1.5% reduction in electricity use would have likely saved US cotton ginners $1,000,000. The goal of this research was to gain a greater understanding of electrical energy consumption patterns in cotton gins and use this knowledge to identify management practices or develop systems that improve energy efficiency. Electrical energy monitoring systems were installed in four gins in 2010. Total power demand and power factor were recorded for the gin during operation. Sensors were also installed to record loads on all individual motors 15 hp and larger. Feed control speeds in the gin were also monitored. All data was recorded at intervals less than 5 s to accurately estimate the effects of downtime and reduced operating efficiency. Data from two of the gins has been analyzed to determine when bales were made and calculate the electrical energy used for each bale. Both gins were more efficient than past surveys indicated. The primary source of variation in the electricity use per bale at each gin was the time required to gin a given bale. The primary implication of this finding for cotton ginners is that gins should be operated at full capacity as much as possible. Additionally, because the power consumed while idling was nearly as large as the power required during ginning, equipment should be turned off if the gin will be idle for several minutes or longer. This time will vary between gins based on warm-up times for dryers, labor requirements for stopping and restarting the gin, and other factors. However, idling times longer than five minutes are likely uneconomical. Low power factor may also be a concern for cotton ginners, if their utility charges a penalty. Data from the additional gins will be analyzed, and the individual motor current data will be examined in greater detail to identify specific situations that decrease energy efficiency.

Technical Abstract: Energy costs are the second largest source of variable costs for cotton gins, accounting for 27% of variable costs. Energy use has typically not been a major consideration in gin design, and previous studies of energy use have utilized instantaneous readings or aggregated season-long values. In this study, electrical energy use was monitored throughout the entire season for several gins across the cotton belt. Motor loads were recorded for gin stands, fans, cleaning machinery, module feeders, and bale presses. Power consumption and power factor were recorded at motor control center disconnects. Additional variables, such as feed control speeds, were monitored when feasible. The gins monitored in 2010 used less than 40 kWh/bale, slightly less than the annual average values reported in past surveys. Differences in electricity use between monitored gins were likely due to differences in layout and installed equipment. Power factor for most gin equipment varied from 0.75-0.80. Power factor at the bale press motor control center rose from 0.50 between bales to 0.85-0.90 when pressing a bale. Gins may benefit from power factor correction if penalized by their utility for low power factor. The primary factor affecting electricity use per bale at a specific gin was the time required to gin a bale. For maximum energy efficiency, cotton ginners should operate at full capacity as much as possible and avoid idling equipment for periods longer than several minutes.